Processes for the preparation of 5-fluoro-1,3-dialkyl-1H-pyrazole-4-carbaldehyde by exchanging chlorine for fluorine (halex processes) are known particularly for 5-chloro-1,3-dialkyl-1H-pyrazole-4-carbonyl chlorides (cf. for example WO 2007/031212 and EP-A 0 776 889).
It is known from WO 2011/061205 that 5-fluoro-1-alkyl-3-fluoroalkyl-1H-pyrazole-4-carbonyl chlorides can be prepared by reacting in a first step 5-chloro-1-alkyl-3-fluoroalkyl-1H-pyrazole-4-carbaldehyde with metal fluorides like KF as fluorinating reagent to obtain 5-fluoro-1-alkyl-3-fluoroalkyl-1H-pyrazole-4-carbaldehyde, followed by a second reaction with a chlorinating agent to obtain the acyl chloride derivatives. Fluorination of pyrazol compounds which are chlorinated on the 5-position and partly or fully fluorinated on the 3-position alkyl are indicated in WO 2011/131615, WO93/11117.
Fluorination of N-Alkyl-3-dichloromethylpyrazolecarboxylate with formation of N-Alkyl-3-difluoromethylpyrazolecarboxylate using HF-complexes of amines is also described (WO 2005044804, WO 2008077907).